rust/src/librustc/middle/trans/adt.rs

642 lines
23 KiB
Rust

// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
/*!
* # Representation of Algebraic Data Types
*
* This module determines how to represent enums, structs, and tuples
* based on their monomorphized types; it is responsible both for
* choosing a representation and translating basic operations on
* values of those types.
*
* Note that the interface treats everything as a general case of an
* enum, so structs/tuples/etc. have one pseudo-variant with
* discriminant 0; i.e., as if they were a univariant enum.
*
* Having everything in one place will enable improvements to data
* structure representation; possibilities include:
*
* - User-specified alignment (e.g., cacheline-aligning parts of
* concurrently accessed data structures); LLVM can't represent this
* directly, so we'd have to insert padding fields in any structure
* that might contain one and adjust GEP indices accordingly. See
* issue #4578.
*
* - Using smaller integer types for discriminants.
*
* - Store nested enums' discriminants in the same word. Rather, if
* some variants start with enums, and those enums representations
* have unused alignment padding between discriminant and body, the
* outer enum's discriminant can be stored there and those variants
* can start at offset 0. Kind of fancy, and might need work to
* make copies of the inner enum type cooperate, but it could help
* with `Option` or `Result` wrapped around another enum.
*
* - Tagged pointers would be neat, but given that any type can be
* used unboxed and any field can have pointers (including mutable)
* taken to it, implementing them for Rust seems difficult.
*/
use core::container::Map;
use core::libc::c_ulonglong;
use core::option::{Option, Some, None};
use core::vec;
use lib::llvm::{ValueRef, TypeRef, True, IntEQ, IntNE};
use middle::trans::_match;
use middle::trans::build::*;
use middle::trans::common::*;
use middle::trans::machine;
use middle::trans::type_of;
use middle::ty;
use syntax::ast;
use util::ppaux::ty_to_str;
/// Representations.
pub enum Repr {
/// C-like enums; basically an int.
CEnum(int, int), // discriminant range
/**
* Single-case variants, and structs/tuples/records.
*
* Structs with destructors need a dynamic destroyedness flag to
* avoid running the destructor too many times; this is included
* in the `Struct` if present.
*/
Univariant(Struct, bool),
/**
* General-case enums: for each case there is a struct, and they
* all start with a field for the discriminant.
*/
General(~[Struct]),
/**
* Two cases distinguished by a nullable pointer: the case with discriminant
* `nndiscr` is represented by the struct `nonnull`, where the `ptrfield`th
* field is known to be nonnull due to its type; if that field is null, then
* it represents the other case, which is inhabited by at most one value
* (and all other fields are undefined/unused).
*
* For example, `core::option::Option` instantiated at a safe pointer type
* is represented such that `None` is a null pointer and `Some` is the
* identity function.
*/
NullablePointer{ nonnull: Struct, nndiscr: int, ptrfield: uint,
nullfields: ~[ty::t] }
}
/// For structs, and struct-like parts of anything fancier.
struct Struct {
size: u64,
align: u64,
packed: bool,
fields: ~[ty::t]
}
/**
* Convenience for `represent_type`. There should probably be more or
* these, for places in trans where the `ty::t` isn't directly
* available.
*/
pub fn represent_node(bcx: block, node: ast::node_id) -> @Repr {
represent_type(bcx.ccx(), node_id_type(bcx, node))
}
/// Decides how to represent a given type.
pub fn represent_type(cx: &mut CrateContext, t: ty::t) -> @Repr {
debug!("Representing: %s", ty_to_str(cx.tcx, t));
match cx.adt_reprs.find(&t) {
Some(repr) => return *repr,
None => { }
}
let repr = @represent_type_uncached(cx, t);
debug!("Represented as: %?", repr)
cx.adt_reprs.insert(t, repr);
return repr;
}
fn represent_type_uncached(cx: &mut CrateContext, t: ty::t) -> Repr {
match ty::get(t).sty {
ty::ty_tup(ref elems) => {
return Univariant(mk_struct(cx, *elems, false), false)
}
ty::ty_struct(def_id, ref substs) => {
let fields = ty::lookup_struct_fields(cx.tcx, def_id);
let ftys = do fields.map |field| {
ty::lookup_field_type(cx.tcx, def_id, field.id, substs)
};
let packed = ty::lookup_packed(cx.tcx, def_id);
let dtor = ty::ty_dtor(cx.tcx, def_id).is_present();
let ftys =
if dtor { ftys + [ty::mk_bool()] } else { ftys };
return Univariant(mk_struct(cx, ftys, packed), dtor)
}
ty::ty_enum(def_id, ref substs) => {
struct Case { discr: int, tys: ~[ty::t] };
impl Case {
fn is_zerolen(&self, cx: &mut CrateContext) -> bool {
mk_struct(cx, self.tys, false).size == 0
}
fn find_ptr(&self) -> Option<uint> {
self.tys.position(|&ty| mono_data_classify(ty) == MonoNonNull)
}
}
let cases = do ty::enum_variants(cx.tcx, def_id).map |vi| {
let arg_tys = do vi.args.map |&raw_ty| {
ty::subst(cx.tcx, substs, raw_ty)
};
Case { discr: vi.disr_val, tys: arg_tys }
};
if cases.len() == 0 {
// Uninhabitable; represent as unit
return Univariant(mk_struct(cx, [], false), false);
}
if cases.all(|c| c.tys.len() == 0) {
// All bodies empty -> intlike
let discrs = cases.map(|c| c.discr);
return CEnum(*discrs.iter().min().unwrap(), *discrs.iter().max().unwrap());
}
if cases.len() == 1 {
// Equivalent to a struct/tuple/newtype.
assert_eq!(cases[0].discr, 0);
return Univariant(mk_struct(cx, cases[0].tys, false), false)
}
// Since there's at least one
// non-empty body, explicit discriminants should have
// been rejected by a checker before this point.
if !cases.iter().enumerate().all(|(i,c)| c.discr == (i as int)) {
cx.sess.bug(fmt!("non-C-like enum %s with specified \
discriminants",
ty::item_path_str(cx.tcx, def_id)))
}
if cases.len() == 2 {
let mut discr = 0;
while discr < 2 {
if cases[1 - discr].is_zerolen(cx) {
match cases[discr].find_ptr() {
Some(ptrfield) => {
return NullablePointer {
nndiscr: discr,
nonnull: mk_struct(cx, cases[discr].tys, false),
ptrfield: ptrfield,
nullfields: copy cases[1 - discr].tys
}
}
None => { }
}
}
discr += 1;
}
}
// The general case.
let discr = ~[ty::mk_int()];
return General(cases.map(|c| mk_struct(cx, discr + c.tys, false)))
}
_ => cx.sess.bug("adt::represent_type called on non-ADT type")
}
}
fn mk_struct(cx: &mut CrateContext, tys: &[ty::t], packed: bool) -> Struct {
let lltys = tys.map(|&ty| type_of::sizing_type_of(cx, ty));
let llty_rec = T_struct(lltys, packed);
Struct {
size: machine::llsize_of_alloc(cx, llty_rec) /*bad*/as u64,
align: machine::llalign_of_min(cx, llty_rec) /*bad*/as u64,
packed: packed,
fields: vec::to_owned(tys)
}
}
/**
* Returns the fields of a struct for the given representation.
* All nominal types are LLVM structs, in order to be able to use
* forward-declared opaque types to prevent circularity in `type_of`.
*/
pub fn fields_of(cx: &mut CrateContext, r: &Repr) -> ~[TypeRef] {
generic_fields_of(cx, r, false)
}
/// Like `fields_of`, but for `type_of::sizing_type_of` (q.v.).
pub fn sizing_fields_of(cx: &mut CrateContext, r: &Repr) -> ~[TypeRef] {
generic_fields_of(cx, r, true)
}
fn generic_fields_of(cx: &mut CrateContext, r: &Repr, sizing: bool)
-> ~[TypeRef] {
match *r {
CEnum(*) => ~[T_enum_discrim(cx)],
Univariant(ref st, _dtor) => struct_llfields(cx, st, sizing),
NullablePointer{ nonnull: ref st, _ } => struct_llfields(cx, st, sizing),
General(ref sts) => {
// To get "the" type of a general enum, we pick the case
// with the largest alignment (so it will always align
// correctly in containing structures) and pad it out.
assert!(sts.len() >= 1);
let mut most_aligned = None;
let mut largest_align = 0;
let mut largest_size = 0;
for sts.each |st| {
if largest_size < st.size {
largest_size = st.size;
}
if largest_align < st.align {
// Clang breaks ties by size; it is unclear if
// that accomplishes anything important.
largest_align = st.align;
most_aligned = Some(st);
}
}
let most_aligned = most_aligned.get();
let padding = largest_size - most_aligned.size;
struct_llfields(cx, most_aligned, sizing)
+ [T_array(T_i8(), padding /*bad*/as uint)]
}
}
}
fn struct_llfields(cx: &mut CrateContext, st: &Struct, sizing: bool)
-> ~[TypeRef] {
if sizing {
st.fields.map(|&ty| type_of::sizing_type_of(cx, ty))
} else {
st.fields.map(|&ty| type_of::type_of(cx, ty))
}
}
/**
* Obtain a representation of the discriminant sufficient to translate
* destructuring; this may or may not involve the actual discriminant.
*
* This should ideally be less tightly tied to `_match`.
*/
pub fn trans_switch(bcx: block, r: &Repr, scrutinee: ValueRef)
-> (_match::branch_kind, Option<ValueRef>) {
match *r {
CEnum(*) | General(*) => {
(_match::switch, Some(trans_get_discr(bcx, r, scrutinee)))
}
NullablePointer{ nonnull: ref nonnull, nndiscr, ptrfield, _ } => {
(_match::switch, Some(nullable_bitdiscr(bcx, nonnull, nndiscr, ptrfield, scrutinee)))
}
Univariant(*) => {
(_match::single, None)
}
}
}
/// Obtain the actual discriminant of a value.
pub fn trans_get_discr(bcx: block, r: &Repr, scrutinee: ValueRef)
-> ValueRef {
match *r {
CEnum(min, max) => load_discr(bcx, scrutinee, min, max),
Univariant(*) => C_int(bcx.ccx(), 0),
General(ref cases) => load_discr(bcx, scrutinee, 0,
(cases.len() - 1) as int),
NullablePointer{ nonnull: ref nonnull, nndiscr, ptrfield, _ } => {
ZExt(bcx, nullable_bitdiscr(bcx, nonnull, nndiscr, ptrfield, scrutinee),
T_enum_discrim(bcx.ccx()))
}
}
}
fn nullable_bitdiscr(bcx: block, nonnull: &Struct, nndiscr: int, ptrfield: uint,
scrutinee: ValueRef) -> ValueRef {
let cmp = if nndiscr == 0 { IntEQ } else { IntNE };
let llptr = Load(bcx, GEPi(bcx, scrutinee, [0, ptrfield]));
let llptrty = type_of::type_of(bcx.ccx(), nonnull.fields[ptrfield]);
ICmp(bcx, cmp, llptr, C_null(llptrty))
}
/// Helper for cases where the discriminant is simply loaded.
fn load_discr(bcx: block, scrutinee: ValueRef, min: int, max: int)
-> ValueRef {
let ptr = GEPi(bcx, scrutinee, [0, 0]);
if max + 1 == min {
// i.e., if the range is everything. The lo==hi case would be
// rejected by the LLVM verifier (it would mean either an
// empty set, which is impossible, or the entire range of the
// type, which is pointless).
Load(bcx, ptr)
} else {
// llvm::ConstantRange can deal with ranges that wrap around,
// so an overflow on (max + 1) is fine.
LoadRangeAssert(bcx, ptr, min as c_ulonglong,
(max + 1) as c_ulonglong,
/* signed: */ True)
}
}
/**
* Yield information about how to dispatch a case of the
* discriminant-like value returned by `trans_switch`.
*
* This should ideally be less tightly tied to `_match`.
*/
pub fn trans_case(bcx: block, r: &Repr, discr: int) -> _match::opt_result {
match *r {
CEnum(*) => {
_match::single_result(rslt(bcx, C_int(bcx.ccx(), discr)))
}
Univariant(*) => {
bcx.ccx().sess.bug("no cases for univariants or structs")
}
General(*) => {
_match::single_result(rslt(bcx, C_int(bcx.ccx(), discr)))
}
NullablePointer{ _ } => {
assert!(discr == 0 || discr == 1);
_match::single_result(rslt(bcx, C_i1(discr != 0)))
}
}
}
/**
* Begin initializing a new value of the given case of the given
* representation. The fields, if any, should then be initialized via
* `trans_field_ptr`.
*/
pub fn trans_start_init(bcx: block, r: &Repr, val: ValueRef, discr: int) {
match *r {
CEnum(min, max) => {
assert!(min <= discr && discr <= max);
Store(bcx, C_int(bcx.ccx(), discr), GEPi(bcx, val, [0, 0]))
}
Univariant(ref st, true) => {
assert_eq!(discr, 0);
Store(bcx, C_bool(true),
GEPi(bcx, val, [0, st.fields.len() - 1]))
}
Univariant(*) => {
assert_eq!(discr, 0);
}
General(*) => {
Store(bcx, C_int(bcx.ccx(), discr), GEPi(bcx, val, [0, 0]))
}
NullablePointer{ nonnull: ref nonnull, nndiscr, ptrfield, _ } => {
if discr != nndiscr {
let llptrptr = GEPi(bcx, val, [0, ptrfield]);
let llptrty = type_of::type_of(bcx.ccx(), nonnull.fields[ptrfield]);
Store(bcx, C_null(llptrty), llptrptr)
}
}
}
}
/**
* The number of fields in a given case; for use when obtaining this
* information from the type or definition is less convenient.
*/
pub fn num_args(r: &Repr, discr: int) -> uint {
match *r {
CEnum(*) => 0,
Univariant(ref st, dtor) => {
assert_eq!(discr, 0);
st.fields.len() - (if dtor { 1 } else { 0 })
}
General(ref cases) => cases[discr as uint].fields.len() - 1,
NullablePointer{ nonnull: ref nonnull, nndiscr, nullfields: ref nullfields, _ } => {
if discr == nndiscr { nonnull.fields.len() } else { nullfields.len() }
}
}
}
/// Access a field, at a point when the value's case is known.
pub fn trans_field_ptr(bcx: block, r: &Repr, val: ValueRef, discr: int,
ix: uint) -> ValueRef {
// Note: if this ever needs to generate conditionals (e.g., if we
// decide to do some kind of cdr-coding-like non-unique repr
// someday), it will need to return a possibly-new bcx as well.
match *r {
CEnum(*) => {
bcx.ccx().sess.bug("element access in C-like enum")
}
Univariant(ref st, _dtor) => {
assert_eq!(discr, 0);
struct_field_ptr(bcx, st, val, ix, false)
}
General(ref cases) => {
struct_field_ptr(bcx, &cases[discr as uint], val, ix + 1, true)
}
NullablePointer{ nonnull: ref nonnull, nullfields: ref nullfields, nndiscr, _ } => {
if (discr == nndiscr) {
struct_field_ptr(bcx, nonnull, val, ix, false)
} else {
// The unit-like case might have a nonzero number of unit-like fields.
// (e.g., Result or Either with () as one side.)
let llty = type_of::type_of(bcx.ccx(), nullfields[ix]);
assert_eq!(machine::llsize_of_alloc(bcx.ccx(), llty), 0);
// The contents of memory at this pointer can't matter, but use
// the value that's "reasonable" in case of pointer comparison.
PointerCast(bcx, val, T_ptr(llty))
}
}
}
}
fn struct_field_ptr(bcx: block, st: &Struct, val: ValueRef, ix: uint,
needs_cast: bool) -> ValueRef {
let ccx = bcx.ccx();
let val = if needs_cast {
let fields = do st.fields.map |&ty| {
type_of::type_of(ccx, ty)
};
let real_llty = T_struct(fields, st.packed);
PointerCast(bcx, val, T_ptr(real_llty))
} else {
val
};
GEPi(bcx, val, [0, ix])
}
/// Access the struct drop flag, if present.
pub fn trans_drop_flag_ptr(bcx: block, r: &Repr, val: ValueRef) -> ValueRef {
match *r {
Univariant(ref st, true) => GEPi(bcx, val, [0, st.fields.len() - 1]),
_ => bcx.ccx().sess.bug("tried to get drop flag of non-droppable type")
}
}
/**
* Construct a constant value, suitable for initializing a
* GlobalVariable, given a case and constant values for its fields.
* Note that this may have a different LLVM type (and different
* alignment!) from the representation's `type_of`, so it needs a
* pointer cast before use.
*
* The LLVM type system does not directly support unions, and only
* pointers can be bitcast, so a constant (and, by extension, the
* GlobalVariable initialized by it) will have a type that can vary
* depending on which case of an enum it is.
*
* To understand the alignment situation, consider `enum E { V64(u64),
* V32(u32, u32) }` on win32. The type has 8-byte alignment to
* accommodate the u64, but `V32(x, y)` would have LLVM type `{i32,
* i32, i32}`, which is 4-byte aligned.
*
* Currently the returned value has the same size as the type, but
* this could be changed in the future to avoid allocating unnecessary
* space after values of shorter-than-maximum cases.
*/
pub fn trans_const(ccx: &mut CrateContext, r: &Repr, discr: int,
vals: &[ValueRef]) -> ValueRef {
match *r {
CEnum(min, max) => {
assert_eq!(vals.len(), 0);
assert!(min <= discr && discr <= max);
C_int(ccx, discr)
}
Univariant(ref st, _dro) => {
assert_eq!(discr, 0);
C_struct(build_const_struct(ccx, st, vals))
}
General(ref cases) => {
let case = &cases[discr as uint];
let max_sz = cases.iter().transform(|x| x.size).max().unwrap();
let discr_ty = C_int(ccx, discr);
let contents = build_const_struct(ccx, case,
~[discr_ty] + vals);
C_struct(contents + [padding(max_sz - case.size)])
}
NullablePointer{ nonnull: ref nonnull, nndiscr, ptrfield, _ } => {
if discr == nndiscr {
C_struct(build_const_struct(ccx, nonnull, vals))
} else {
assert_eq!(vals.len(), 0);
let vals = do nonnull.fields.mapi |i, &ty| {
let llty = type_of::sizing_type_of(ccx, ty);
if i == ptrfield { C_null(llty) } else { C_undef(llty) }
};
C_struct(build_const_struct(ccx, nonnull, vals))
}
}
}
}
/**
* Building structs is a little complicated, because we might need to
* insert padding if a field's value is less aligned than its type.
*
* Continuing the example from `trans_const`, a value of type `(u32,
* E)` should have the `E` at offset 8, but if that field's
* initializer is 4-byte aligned then simply translating the tuple as
* a two-element struct will locate it at offset 4, and accesses to it
* will read the wrong memory.
*/
fn build_const_struct(ccx: &mut CrateContext, st: &Struct, vals: &[ValueRef])
-> ~[ValueRef] {
assert_eq!(vals.len(), st.fields.len());
let mut offset = 0;
let mut cfields = ~[];
for st.fields.eachi |i, &ty| {
let llty = type_of::sizing_type_of(ccx, ty);
let type_align = machine::llalign_of_min(ccx, llty)
/*bad*/as u64;
let val_align = machine::llalign_of_min(ccx, val_ty(vals[i]))
/*bad*/as u64;
let target_offset = roundup(offset, type_align);
offset = roundup(offset, val_align);
if (offset != target_offset) {
cfields.push(padding(target_offset - offset));
offset = target_offset;
}
let val = if is_undef(vals[i]) {
let wrapped = C_struct([vals[i]]);
assert!(!is_undef(wrapped));
wrapped
} else {
vals[i]
};
cfields.push(val);
offset += machine::llsize_of_alloc(ccx, llty) as u64
}
return cfields;
}
fn padding(size: u64) -> ValueRef {
C_undef(T_array(T_i8(), size /*bad*/as uint))
}
// XXX this utility routine should be somewhere more general
#[inline]
fn roundup(x: u64, a: u64) -> u64 { ((x + (a - 1)) / a) * a }
/// Get the discriminant of a constant value. (Not currently used.)
pub fn const_get_discrim(ccx: &mut CrateContext, r: &Repr, val: ValueRef)
-> int {
match *r {
CEnum(*) => const_to_int(val) as int,
Univariant(*) => 0,
General(*) => const_to_int(const_get_elt(ccx, val, [0])) as int,
NullablePointer{ nndiscr, ptrfield, _ } => {
if is_null(const_struct_field(ccx, val, ptrfield)) { 1 - nndiscr } else { nndiscr }
}
}
}
/**
* Extract a field of a constant value, as appropriate for its
* representation.
*
* (Not to be confused with `common::const_get_elt`, which operates on
* raw LLVM-level structs and arrays.)
*/
pub fn const_get_field(ccx: &mut CrateContext, r: &Repr, val: ValueRef,
_discr: int, ix: uint) -> ValueRef {
match *r {
CEnum(*) => ccx.sess.bug("element access in C-like enum const"),
Univariant(*) => const_struct_field(ccx, val, ix),
General(*) => const_struct_field(ccx, val, ix + 1),
NullablePointer{ _ } => const_struct_field(ccx, val, ix)
}
}
/// Extract field of struct-like const, skipping our alignment padding.
fn const_struct_field(ccx: &mut CrateContext, val: ValueRef, ix: uint)
-> ValueRef {
// Get the ix-th non-undef element of the struct.
let mut real_ix = 0; // actual position in the struct
let mut ix = ix; // logical index relative to real_ix
let mut field;
loop {
loop {
field = const_get_elt(ccx, val, [real_ix]);
if !is_undef(field) {
break;
}
real_ix = real_ix + 1;
}
if ix == 0 {
return field;
}
ix = ix - 1;
real_ix = real_ix + 1;
}
}
/// Is it safe to bitcast a value to the one field of its one variant?
pub fn is_newtypeish(r: &Repr) -> bool {
match *r {
Univariant(ref st, false) => st.fields.len() == 1,
_ => false
}
}